The present invention relates to a data storage system coupled or connected to a plurality of host processors. More particularly, the invention is concerned with a technology which can effectively be adopted for enhancing efficiency of exclusive control for the processing of stored data.
In general, there exist a plurality of files in one volume set up in a magnetic disk drive or device. When a file in a given volume is being used by a given host processor, the volume containing that file assumes a device busy state. As a result of this, access of other host processor to the other file contained in the given volume is forced to wait for releasing of the volume from the device busy state. This is because such exclusive use is effectuated that when one host processor is using one volume, any other host processor is disabled to use that volume.
With the access control scheme mentioned above, there arises a problem that when a plurality of files exist on a given volume, files other than that for which the exclusion is to be effectuated are unnecessarily subjected to the exclusion, which leads to degradation of file utilization efficiency. For solving the problem mentioned above, there has been proposed such approach that a control memory is provided in a magnetic disk control unit for storing information indicating on a file-by-file basis whether or not individual files are being used, wherein the use statuses of the files are checked by a host processor system by reading the above-mentioned information from the corresponding control memory, as disclosed, for example, in JP-B-1-15899. In the file access control scheme disclosed in JP-B-1-15899, the exclusive control is performed on a logical-file basis. Consequently, when sharing of a same file is desired, e.g. when a same file is to be shared by two host processors only for read operation, such sharing of the same file is impossible because of the exclusion on a file-by-file basis.
Further, JP-A-7-200179 discloses a scheme according to which a physical volume is partitioned into a plurality of subvolumes. With the volume management scheme disclosed in JP-A-7-200179, the exclusive control can be carried out on a subvolume basis. In that case, the subvolume itself has to be created upon formatting of the disk. Further, the exclusive control of the subvolumes is performed by the host processor by confirming or checking the use status of the subvolumes on the basis of information held by an external storage.
In the conventional systems described above, for effectuating the exclusive control on the basis of files contained in a physical volume or on a subvolume basis, it becomes necessary that the host processing system reads from the magnetic disk device the information indicating whether or not the files or subvolumes are being used, to thereby check whether the file or subvolume of concern is being used or not, which in turn means that the host processing has to be imparted with an especial function for the exclusive control. For realizing such exclusive control, alteration or modification of both host software and the server storage control unit becomes necessary.